1. Technical Field of the Invention
This invention relates to a circuit breaker capable of breaking a circuit when an excess current or a short-circuit current flows in a load side, and more particularly to a circuit breaker in which mechanical portions within a casing are electrically insulated from a main circuit to prevent a high voltage from being induced to the mechanical portions.
2. Description of Prior Art
A circuit breaker is a switching gear for automatically breaking a circuit when a short-circuit accident occurs in such a portion as a power transmission-distribution line, a bus bar and equipment in a transformer station, etc. It also breaks the circuit when an excess current flows in a load side. In addition, it is not only used in breaking the circuit, 11 but also used for opening and closing the circuit in a normal condition. In order to protect the circuit, reliable breaking for short-circuit current and excess current is required.
In a conventional circuit breaker as disclosed in FIGS. 16, 20 and 60 of Japanese Patent Unexamined Publication No. 61-151945 (Japanese Patent Examined Publication No. 7-27750), a switching mechanism, provided at a central pole, is mechanically connected through a lower lever to a movable contact carrier at the central pole. An overcurrent tripper within an accessory chamber is provided at each pole, and is fixed to a conductor of each pole.
In the above conventional technique, the switching mechanism, the lower lever and the overcurrent tripper are made of metal. Therefore, the switching mechanism is electrically charged to a potential substantially equal to that of the movable contact carrier at the central pole, and the overcurrent tripper is electrically charged to a potential substantially equal to that of the conductor of each pole. Therefore, when a cover of the circuit breaker is opened exceptionally in a hot-line condition (usually, opening the cover is carried out after interrupting the power) to gain access within the accessory chamber of the circuit breaker, e.g., for adding or exchanging an interior accessory, charged portions of the switching mechanism or that of the overcurrent tripper are especially exposed and may result in accidental user contact, which raises a problem of a dangerous condition.
Particularly dangerous are arrangements which provide some degree of isolation of the circuit, but which still have small main circuit exposure within the accessory chamber. More particularly, electrical workers are lulled into a false sense of safety by the partial (i.e., less than perfect) isolation of the main circuit and thus become more carefree and careless. Eventually such carefree behavior will result in accidential contact with the small exposed main circuit resulting in harm to the electrical worker. Examples of such dangerous partial isolation can be seen in U.S. Pat. No. 5,281,776 Morel et al. and U.S. Pat. No. 5,310,971 Vial et al., which dangerously leave a terminal portion of the main circuit contact terminal strip 25 (FIG. 3 of U.S. Pat. No. 5,281,776) electrically exposed within an accessory chamber. Further related patents are U.S. Pat. Nos. 5,357,066 and 5,298,874. The teachings of all mentioned references are incorporated herein by reference.
It is a first object of this invention to provide a circuit breaker which eliminates the risk of an electric shock, thereby providing excellent safety.
It is a second object of this invention to provide a circuit breaker having a sufficient durability for i.e., being capable of withstanding a high internal pressure when a short-circuit current occurs at a load side.
It is a third object of this invention to provide a circuit breaker capable of preventing an accessory cover from being handled i.e., removed or accessed by an unauthorized person.
It is a fourth object of this invention to provide a circuit breaker capable of installing or removing interior accessories without removing a main cover plate disposed so as to cover the surface of the circuit breaker in a switch box where the circuit breaker is installed.
It is still a further object of this invention to avoid electrical connection between a main circuit and a tripping mechanism, by instead providing interaction therebetween in the form of an electrical magnetic flux transmitted through a main circuit case.
In order to provide the above and other objects and advantages, the present invention is a circuit breaker comprising a main circuit including a power-side stationary conductor electrically connected to a power-side terminal, a load-side stationary conductor electrically connected to a load-side terminal, and a movable conductor electrically connecting and disconnecting said power-side stationary conductor and said load-side stationary conductor; an opening-closing mechanism mechanically connected to the movable conductor; a main circuit case totally isolating the main circuit from exposure in an accessory chamber and made of an insulating material; and a trip device for causing the opening-closing mechanism to break the main circuit when a current in the main circuit exceeds a threshold value, wherein the opening-closing mechanism and the trip device are electrically insulated from the main circuit.
In another embodiment, the present invention is a circuit breaker comprising a main circuit including a power-side stationary conductor electrically connected to a power-side terminal, a load-side stationary conductor electrically connected to a load-side terminal, and a movable conductor electrically connecting said power-side stationary conductor and the load-side stationary conductor together on an ON operation; an opening-closing mechanism disposed outside of the main circuit case and mechanically connected to open-close the movable conductor, a main circuit case containing the main circuit and tatally isolating the same from exposure within an accessory chamber; and a trip device for causing the opening-closing mechanism to break electrical conduction along said main circuit when a current in the main circuit exceeds a threshold value, wherein the main circuit case is made of an insulating material, and the opening-closing mechanism is connected to the moving conductor through an insulating material.
In a third embodiment, the present invention is a circuit breaker comprising a main circuit including a power-side stationary conductor electrically connected to a power-side terminal, a load-side stationary conductor electrically connected to a load-side terminal, and a movable conductor electrically connecting the power-side stationary conductor and the load-side stationary conductor together on an ON operation; an opening-closing trip mechanism mechanically connected to the movable conductor; a main circuit case containing the main circuit and tatally isolating the same from exposure within an accessory chamber; and a trip device for causing the opening-closing mechanism to break the main circuit when a current in the main circuit exceeds a threshold value; wherein the main circuit case is made of an insulating material and the opening-closing mechanism is disposed outside of the main circuit case, and is electrically insulated from the main circuit, and the trip device includes a transmission mechanism for transmitting an operation of the trip device to the opening-closing mechanism, and the transmission mechanism is disposed outside of the main circuit case, and is electrically insulated from the main circuit.
In yet an additional embodiment, the present invention is a circuit breaker comprising a breaker casing; a main circuit including a power-side stationary conductor electrically connected to a power-side terminal, a load-side stationary conductor electrically connected to a load-side terminal and a movable conductor electrically connecting and disconnecting the power-side stationary conductor and said load-side stationary conductor; an opening-closing mechanism mechanically connected to the movable conductor; a main circuit case containing the main circuit so as to tatally isolate the main circuit from exposure within an accessory chamber and being made of an insulating material; a trip device for causing the opening-closing mechanism to break the main circuit when a current in the main circuit exceeds a threshold value; an accessory area disposed within the casing for accomodating installation of an interior accessory; and an accessory cover disposed on a surface of the casing for covering the accessory area; wherein the opening-closing mechanism, the main circuit case, and the trip device are disposed in the casing, and the opening-closing trip mechanism and the trip device are electrically insulated from the main circuit.
In present invention, since the opening-closing mechanism is electrically insulated from the main circuit, a voltage on the main circuit is not conducted to the opening-closing mechanism. Further, since the main circuit case is constructed to totally isolate the main circuit from exposure within an accessory area, total main circuit isolation is provided. Therefore, a circuit breaker capable of reducing a risk of electrical shock is obtained.